1. Field of the Invention
The invention relates to thermal afterburning systems and more particularly to such systems using a plurality of combustion chambers and concentrically arranged counterflow cooling ducts for mixing the engine exhaust gases with air and for cooling the burned exhaust gases and toxic contaminants.
2. Prior Art
The invention represents an improved thermal afterburning system over that disclosed in U.S. Pat. No. 3,989,469. That prior art thermal afterburner consists of the following basic components. An elongated counterflow combustion chamber receiving exhaust gases to be afterburned and additional combustion air. A cooling air chamber encircling the combustion chamber and directing heated cooling air into the combustion chamber. The combustion chamber includes a discharge chamber at the downstream end thereof, and a number of ducts having relatively small cross-section and separated from one another are connected to the discharge chamber for discharge of afterburned exhaust gas therefrom. The ducts have a wall forming a joint heat exchange surface with an outer wall of the cooling air chamber such that the ducts are separated from the combustion chamber over their entire length.
Such a counterflow cooling system has given rise to serious manufacturing problems, because the creation of thin pipelines from chrome steel which, simultaneously with a surrounding air chamber, have direct heat-exchange surfaces, is very expensive and heat-expansion phenomena have occurred in the apparatus which have led to crack formation.
Furthermore, the process of mixing exhaust gas and supplementary air in a single counterflow combustion chamber has not been intensive, thus necessitating exceedingly large combustion chambers.
Also, "lean" carburetor adjustment in the engines which, particularly in the partial-load operating region, are set with .lambda.=.+-.1.1 has not produced sufficient post-combustion energy to maintain the thermal equilibrium inside the combustion chamber.
Finally, steps have to be taken to remove the sooty carbon deposit in addition to the reduction of CO, HC and NO.sub.x.